Aquaculture sector of Pakistan is suffering with infectious diseases caused by microbial pathogens.
Predominantly these pathogens have bacterial origin and among those, Aeromonas hydrophila causes majority of the diseases.
The gram-negative A. hydrophila is pervasive in freshwater causing abdominal dropsy in farmed fish. Diseases caused by A. hydrophila are the major cause of fish mortality resulting economic loss.
Use of antibiotic drugs for killing or inhibiting microbial processes has certain limitations and disadvantages.
Vaccines are better alternatives of antibiotic drugs to prevent the diseases. Aquaculture vaccines are being practiced in developed countries for more than two decades.
In Pakistan, vaccination has been seen for humans and veterinary animals but no precedence exists for use of vaccines in aquaculture.
No particular defensive product against Aeromonas hydrophila is available in Pakistan and many countries of Asia.
The present research work was aimed at preparing and evaluating efficacy of inactivated fish vaccines against local strains of A. hydrophila.
The bacterial isolates were obtained from diseased Labeorohita (Rohu) collected from different fish farms in Punjab.
Morphological characterization was performed in which size, structure, appearance and shape of bacterial colonies were observed through biochemical tests.
Molecular characterization, Polymerase Chain Reaction (PCR) and genomic DNA amplification was performed which confirmed isolates as hydrophilaharboring pathogenic genes.
For vaccine trials, two parallel vaccination experiments were conducted in pond environment for Rohu, Mori and Grass carp species administered with inactivated vaccines having alum-precipitate and Montanide oil as adjuvants.
Significantly high degree of antibody titers were observed in vaccinated groups as compared to unvaccinated groups (Control).
No adverse impact on growth of fishes was observed due to alum-precipitated vaccine injection whereas soil-based vaccination experiment presented significant increase in growth rate of vaccinated groups.
The post-vaccination challenge study also revealed that fish mortality was significantly low in vaccinated groups in both experiments.
To the best of our knowledge, the present work is premier step towards the development of vaccines for cultured fishes in Pakistan. Many dimensions of further experimentation existto promote fish immunology research and development in the country. In current experiment, efficacy of vaccines has been tested for Rohu, Mori and Grass carp.
Immune response and growth performance of other fish species such as Silver carp and Thela can be readily investigated with vaccines prepared in present study on similar lines.
In particular, the A. hydrophila isolates of present study may be used for future research towards disease prevention against local strains of A. hydrophila in aquacultures sector. Development of autogenous aquaculture vaccines against A. hydrophila and their commercialization may be a potential research area to focus in future.
We are highly grateful to acknowledge Pakistan Science Foundation (PSF), Islamabad who provided financial assistance to complete PhD research work through a project entitled “Isolation, Molecular Characterization of Pathogenic Bacteria and Development of Fish Vaccine for Culturable Fish Species of Pakistan” under Grant no. PSF/NSLP/P-UVAS (701) at Department of Fisheries and Aquaculture, University of Veterinary and Animal Sciences, Lahore, Pakistan. The writers are PhD student at University of Veterinary and Animal Sciences, Lahore